1. Field of the Invention
The present invention relates to a liquid supply apparatus, more particularly to a portable liquid supply apparatus that is constructed so that liquid medicine, etc. is supplied in a constant quantity per unit time.
2. Description of the Related Art
There are a number of cases where certain kinds of medicine should be injected into a patient in a constant quantity per unit time and over a long period of time. The example of the medicine is an anodyne that is dosed to a patient feeling serious pain. Unless the anodyne is dosed to a patient in a constant quantity per unit time, the patient may feel pain.
An apparatus for injecting such a medicine by pushing, in a constant speed, a plunger of a common syringe mounted to the apparatus, is known. It is unsuitable for a patient to carry the conventional apparatus due to its large size.
A kind of a medicine injection apparatus capable of being carried by a patient is currently being used. The portable medicine injection apparatus is a structure in which a resilient bladder made of rubber material is provided in a cylindrical chamber. An inlet and an outlet are formed on the resilient bladder. The bladder inflates as the medicine is injected thereinto through the inlet. A small tube is attached to the outlet through which the medicine gradually draws off. The medicine (an injection) is discharged in a small amount and injected in droplet form at a site, such as a vein or an epidural space of a patient, where a medical doctor targets.
In a medicine injection apparatus using its resiliency, the resilient bladder may cause some problems. Inferior goods, in which thickness of the bladder is not uniform and fine holes are formed thereon, may be manufactured. The inferiority affects the resiliency of the bladder which, in turn, cannot have the desired resiliency. If this is the case, it is impossible to dose the medicine to the patient in a constant quantity per unit time. Furthermore, a medical doctor cannot beforehand treat the inferiority since it is usually discovered during the use of the bladder.
A medicine injection apparatus using a bladder and an elastic body is proposed. The resilient bladder or elastic body has such a problem that its resiliency or elasticity may be varied in accordance with the quantity of the medicine contained therein. There is also the following shortcoming. That is, the medicine is injected into the bladder or body in an excessively larger quantity than the doctor targets since an external force (elasticity of the elastic body) affecting on a liquid flow is too large at an early period of the injection, whereas the medicine is injected in an amount much smaller than the target at a late period of the injection since the external force is too small.